Tuesday, January 8, 2013

New paper finds another mechanism by which the Sun controls climate

A paper published today in Climate of the Past finds that changes in both solar activity and the Earth's orbit "lead to changes in surface temperature and in...precipitation" and that both of these changes interact with feedbacks to produce complex patterns of climate change. According to the authors,

"We conclude from our simulation results that non-linear effects and feedbacks of the orbital and solar activity forcing substantially alter the δ18O [an oxygen isotope proxy for both temperature and precipitation] in precipitation pattern and its relation to temperature change."

The paper also shows solar activity [TSI] at the end of the 20th century was near the highest levels of the past 10,000 years. The paper shows average total solar irradiance [TSI] at the Earth surface increased by about 1.2 Wm-2 from the Maunder Minimum 300 years ago to the end of the 20th century, dwarfing the alleged effect of CO2 over the same time period [about 0.3 Wm-2 at the Earth surface]. Note it is not necessary to subtract albedo as the proxy for TSI at the Earth surface already incorporates the albedo.The authors discuss possible mechanisms by which changes in solar activity can be greatly amplified to cause climate change, including

"A plausible physical mechanism how solar activity might alter the state of the middle atmosphere via UV radiation and how this change is transported to the troposphere is explained by a number of studies (Gray et al., 2010; Ineson et al., 2011; Kuroda and Kodera, 2002; Shindell et al., 2001; Spangehl et al., 2010).These studies conclude that an increase of UV radiation during periods of high solar activity heat the middle atmosphere due to photochemical reactions with stratospheric ozone. This leads to an altered stratospheric circulation that propagates pole and downwards to affect tropospheric jet streams and thus atmospheric circulation on a synoptic scale [large scale]."

From the paper:

The inﬂuence of the solar activity on Earth’s climate is still under discussion (Gray et al., 2010; Haigh, 1994; Lockwood, 2012; Magny et al., 2004; Wanner et al., 2008). Several reviews on this topic have recently been published (Beer et al., 2006; Gray et al., 2010; Haigh, 2003, 2007; Jager, 2008; Lockwood, 2012; Rind, 2002). A plausible physical mechanism how solar activity might alter the state of the middle atmosphere via UV radiation and how this change is transported to the troposphere is explained by a number of studies (Gray et al., 2010; Ineson et al., 2011; Kuroda and Kodera, 2002; Shindell et al., 2001; Spangehl et al., 2010). These studies conclude that an increase of UV radiation during periods of high solar activity heat the middle atmosphere due to photochemical reactions with stratospheric ozone. This leads to an altered stratospheric circulation that propagates pole and downwards to affect tropospheric jet streams and thus atmospheric circulation on a synoptic scale [large scale weather systems]. As a plausible consequence the studies by Lockwood et al. (2010) and Wolling et al. (2010) found an increase of atmospheric blocking during solar minima that accounts for unusual low temperatures over Europe and simultaneous warming over Greenland, emphasizing that solar activity might trigger climate on a regional scale, only. Further studies (e.g. Martin-Puertas et al., 2012) have shown the occurrence of atmospheric circulation pattern similar to a negative NAO phase during periods with less solar activityClim. Past, 9, 13-26, 2013www.clim-past.net/9/13/2013/doi:10.5194/cp-9-13-2013Influence of orbital forcing and solar activity on water isotopes in precipitation during the mid- and late Holocene

S. Dietrich1, M. Werner1, T. Spangehl2, and G. Lohmann11Alfred Wegener Institute for Polar and Marine Research, Bussestr. 24, 27570 Bremerhaven, Germany2Deutscher Wetterdienst, Frankfurter Str. 135, 63067 Offenbach, GermanyAbstract. In this study we investigate the impact of mid- and late Holocene orbital forcing and solar activity on variations of the oxygen isotopic composition in precipitation. The investigation is motivated by a recently published speleothem δ18O record from the well-monitored Bunker Cave in Germany. The record reveals some high variability on multi-centennial to millennial scales that does not linearly correspond to orbital forcing. Our model study is based on a set of novel climate simulations performed with the atmosphere general circulation model ECHAM5-wiso enhanced by explicit water isotope diagnostics. From the performed model experiments, we derive the following major results: (1) the response of both orbital and solar forcing lead to changes in surface temperatures and δ18O in precipitation with similar magnitudes during the mid- and late Holocene. (2) Past δ18O anomalies correspond to changing temperatures in the orbital driven simulations. This does not hold true if an additional solar forcing is added. (3) Two orbital driven mid-Holocene experiments, simulating the mean climate state approximately 5000 and 6000 yr ago, yield very similar results. However, if an identical additional solar activity-induced forcing is added, the simulated changes of surface temperatures as well as δ18O between both periods differ. We conclude from our simulation results that non-linear effects and feedbacks of the orbital and solar activity forcing substantially alter the δ18O in precipitation pattern and its relation to temperature change.